On the PSPice OrCAD, how do you add a diode with a 0.7V forward bias and a unknown voltage source?
PSpice OrCAD Adding Diode and Unknown Source
diodessourcevoltage
Related Solutions
My, that's a lot of questions.
Presumably the diode model you instructor wants you to use is an ideal diode with 0.7V drop in series with a 4 ohm resistor. So, when the diode is conducting, it behaves like a voltage source with a resistor in series. When the forward bias is less than 0.7V it does not conduct.
Is the 4 ohms per diode negligible in comparison to 1.5K? Well, it's more than 0.5% for two diodes so it will drop tens of mV. That might be negligible or it might not be, depending on the application. Since the instructor gives you the value, I suggest it might not be negligible in terms of getting the correct answer.
Two such diodes in series behave like one 1.4V diode with 8 ohms in series.
Since it is clear that the diode is forward biased, it acts as a short circuit but with a constant voltage drop. So you can replace the diode with a 0.7V and the circuit can be redrawn as shown.
simulate this circuit – Schematic created using CircuitLab
Now it is just a matter of writing and solving two linear equations.
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Best Answer
This is my interpretation of your question. I might be tackling this the wrong way.
I think you've got some circuits around a diode and you want to find what the input voltage has to be for the diode voltage to be 700mV. I just tried a simple series resistor and diode.
I drew the circuit in Orcad Capture and didn't specify the voltage on the source:
Then I set up a simulation profile to sweep the voltage source over a range of voltages:
Finally, I plotted the voltage across the diode and used the cursor to find where the diode voltage was 700mV. I found that V1 = 1.88V at this point.
Maybe you can take this idea and apply it to whatever circuits you're analyzing.